Journal of Lipid Research, Vol 27, 629-636, Copyright © 1986 by Lipid Research, Inc.
Different metabolic rates for arachidonoyl molecular species of ethanolamine glycerophospholipids in rat brain
Y Nakagawa and LA Horrocks
The ethanolamine glycerophospholipids (EGP) contain most of the
arachidonate (20:4, n-6) and adrenate (22:4, n-6), potential precursors of
biologically potent prostaglandins and related compounds. Much better
methods utilizing high performance liquid chromatography (HPLC) techniques
are now available for the study of the molecular species of all three
classes, namely diacyl, alkenylacyl (plasmalogen), and alkylacyl. Different
molecular species may have different functions. This possibility was
studied by examining the rates of incorporation of [3H]arachidonic acid
into the three major molecular species of each of the three classes of
ethanolamine glycerophospholipids. After the intracerebral injection of
[3H]20:4 into rat brain, it was rapidly converted to 22:4(n-6). Of the
total radioactivity, 10-20% was located in 22:4 in alkenylacyl and
diacyl-GPE. In the alkylacyl-GPE, labeled 22:4 was preferentially
incorporated and accounted for 50-60% of the total radioactivity. The
primary arachidonoyl molecular species of alkenylacyl, alkylacyl, and
diacyl-GPE were the 18:1-20:4, 16:0-20:4, and 18:0-20:4 species. The
alkylacyl class contained almost equal proportions of these three molecular
species. On the other hand, the 20:4 in alkenylacyl and diacyl classes was
combined largely with 18:0 groups at the sn-1 position. In particular, the
18:0-20:4 species comprised about 80% of arachidonoyl molecular species of
the diacyl class. In all three classes, the highest specific
radioactivities were found in the 18:1-20:4 species, whereas the 18:0-20:4
species had the lowest specific radioactivity. Over the period 60 min-24
hr, the diacyl 18:0-20:4 and all three arachidonoyl molecular species of
the alkenylacyl class increased in specific radioactivity more rapidly than
the other arachidonoyl molecular species.
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